question on P25 noise

[kjfswkr]

Hi all,
I am on the fire department and have some police frequencies programmed into my P-25 Icom radio. Say I am listening to lebanon, NH and after the office talks I hear a lound squelch trail noise. This happens after every transmission so needless to say I don't listen often to Lebanon because of the noise. It also seems to be doing it on Franklin, NH PD dispatch now but not so often. Anyone have any idea? Perhaps I don't have something programed correct?

73'

kevin

 

[W2NJS]

Find out if your Icom has a feature called "reverse burst." If it does, turn it on in the CPS and see if the annoying itail s eliminated. You may find two settings for the burst, I think they're either 120 or 180, so try both. This all assumes that the PD is transmitting a reverse burst. You can find out if they are by watching your RSS indicator on the radio's display; the radio will show a secondary RF "pop" transmission right after the regular transmission shuts off. Tech data explaining more about how this feature works can be found via Google.

 

[kjfswkr]

Thanks, will give it a try.

 

[Avery93]

According to the database those two departments are P25 digital, so CTCSS reverse burst is not an issue (Icoms are only capable of 180° burst anyway).

kjfswkr: Can you describe the sound more accurately? Does it actually sound like squelch (white noise) or is it more of a "thunk" or "pop"? If the base radios are using a desktop microphone (like this), I have noticed the "kerchunk" sound they often make when unkeyed is amplified and distorted when using P25. It can almost sound like dropping a large object onto something. The mobile microphones can also make a sliding type sound when unkeyed that can be vocoded funny as well. If the sound is anything like this then there isn't really anything you can do about it. Icoms (or at least the F70/80) don't have Automatic Gain Control, the one feature that might help.

Now if the noise is actually squelch or white noise, then one possibility is the channels are programmed as mixed-mode (both analog & digital receive) and your squelch is set too low. However this should only happen if the channels are programmed for mixed-mode and the analog side is carrier squelch (no CTCSS/DCS). Can you tell us exactly when you hear the sound? For example as soon as a radio unkeys, or after the repeater drops out etc...

 

[mainetrunk]

I hear a weird p25 signal too. It sounds like someone is tapping the mic 20 times fast. I speak of Strafford South-155.7975-nac-ABE.